Typical magnetic read/write configurations have the magnetic storage media, a flat magnetic disc, mounted rotatably in close proximity to a magnetic transducer head and its corresponding support structure. In high capacity devices, the discs are rotated at high speeds to create an air cushion or bearing that supports each transducer head at a controlled distance from the disc, called the flying height, or fly height.
A general trend in magnetic storage media is to increase the storage density of the medium. As the storage density increases, the transducer head must be flown closer to the medium so that it can distinguish between adjacent storage areas on the medium. However, the fly height has to be high enough so that the head does not contact the surface of the storage medium. With the advances in storage media in recent years, the fly height has necessarily been reduced from about 0.25 μm to less than about 0.01 μm. At such low fly heights, a number of factors can affect performance of the transducer. These factors include surface roughness, structural variations of the transducer, and structural variations of the support structure of the transducer.
During the use of magnetic storage medium, the temperature of the storage medium, the transducer, and the supporting structure of the transducer increases. At low fly heights, effects from this temperature change, also called thermal effects, can have an impact on transducer performance. Thermal effects include the expansion of a material when its temperature increases. The expansion of a material when heated can be quantified by a temperature coefficient of thermal expansion (CTE). Materials with a higher coefficient of thermal expansion expand more in response to a given temperature increase.
The CTE of a material can vary at different temperatures. For materials used in magnetic recording heads, the relevant CTE of the material is the CTE within normal head operating temperatures. Generally, normal head operating temperatures range from room temperature to about 150° C. The term CTE as used throughout this specification is understood to mean the CTE within normal head operating temperatures.
Generally, the transducer is recessed from the air bearing surface (ABS). As the temperature of the storage media and the transducer increases, the material of the transducer will expand and protrude with respect to the ABS. This results in the transducer being closer to the storage media at higher temperatures and farther away at lower temperatures. This phenomena is referred to as the Thermal Pole Tip Recession (T-PTR).
In order to attain a low fly height without contact between the head and the medium under all operating temperatures, the T-PTR should be low. Variation of transducer recession with temperature may not only significantly impact the transducer's electrical and fly performance but it may also cause extensive thermal asperities and head crash at higher temperatures. With increasing recording areal density and correspondingly decreasing fly heights, the change in head-media spacing due to temperature effects has a more pronounced effect.
In a typical recording head the magnetic shields of the transducer are made from a Ni Fe alloy with a composition close to about 20% Fe and 80% Ni. This composition has very good magnetic shielding properties, but has a very large CTE of about 12 to 13×10−6/° C. Other configurations of magnetic recording heads use Sendust as a bottom shield material, this material also has an unacceptably high CTE from 12 to 17×10−6/° C. (from G. Stoney, Proc Roy. Sco. London, A82, pp. 172 and H. Shibaya and I. Fukuda, IEEE Trans. Mag. V13 no. 4, 1977 pp. 1029). Because of these high CTEs, the shields of the transducer are the major contributor to T-PTR and the resulting temperature dependent variations of head-media spacing.
In order to attain reliable magnetic recording heads with very low fly heights, the contribution of the magnetic shields to T-PTR must be minimized. Current magnetic recording heads do not minimize this contribution and consequently there remains a need for a magnetic recording head with shields that have a smaller contribution to T-PTR.